The present invention relates to balloon dilation catheters. In particular, the invention relates to over-the-wire and non-over-the-wire catheters used for angioplasty.
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for expanding a constricted area or stenoses in coronary arteries. It is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, a physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. While the catheter is being steered through the vascular system, the balloon is in a deflated state, wrapped (i.e., folded) tightly about the distal end of the catheter to reduce the profile of the balloon so that it can easily traverse arterial vessels and stenoses having small through openings. When the catheter is positioned with the balloon across the stenosis, the balloon is inflated by supplying fluid under pressure through an inflation lumen to the balloon. Inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish an acceptable blood flow through the artery.
Over-the-wire catheters and non-over-the-wire catheters are two types of dilatation catheters that are commonly used in angioplasty. One type of over-the-wire catheter has an inflation lumen (defined by an outer tube) in fluid flow communication with a balloon member, and a guide wire lumen (defined by an inner tube) through which a separate flexible guide wire is advanced to establish a path to the stenosis. Once a distal end of the guide wire is across the stenosis, the separate over-the-wire catheter is advanced over the guide wire until the balloon is positioned across the lesion.
Typically, the balloon member of the over-the-wire catheter is bonded to the inner tube that defines the guide wire lumen. This bonded region at the distal end of the over-the-wire catheter is a relatively stiff section of an otherwise flexible catheter. The flexible guide wire usually includes an extremely flexible radiopaque spring tip at its distal end. The extreme flexibility of the spring tip allows the guide wire to be steered into and through tortuous arterial branches. Because the relatively stiff bonded region of the over-the-wire catheter is located proximal to the extremely flexible spring tip, there is a potential stress concentration point on the guide wire between the stiff bonded region and the flexible spring tip. Due to the tortuosity of the vascular system through which the guide wire is steered, the guide wire may develop a kink or may weaken due to fatiguing at this stress concentration point. These occurrences may make the guide wire difficult to steer and may unnecessarily prolong the angioplasty procedure.
One type of non-over-the-wire catheter has its own built in flexible guide wire (often referred to as a core wire), such that the core wire, balloon and inflation lumen comprise a single unit. The single unit construction of the non-over-the-wire catheter requires that the catheter be advanced as one element through a patient's vascular system, so as to position the balloon across the lesion. Typically, in a non-over-the-wire catheter, the balloon member is bonded directly to the core wire or to an inner sleeve that is in turn bonded to the core wire. As in the over-the-wire catheter, this bonded region at the distal end of the non-over-the-wire catheter is relatively stiff. Similar to the guide wire of the over-the-wire catheter, the distal end of the flexible core wire of the non-over-the-wire catheter usually includes an extremely flexible radiopaque spring tip. The extreme flexibility of the spring tip allows the non-over-the-wire catheter to be steered into and through tortuous arterial branches. Because the relatively stiff bonded region of the non-over-the-wire catheter is located proximal to the extremely flexible spring tip (as in the over-the-wire catheter), there is a potential stress concentration point on the core wire between the stiff bonded region and the flexible spring tip. Due to the tortuosity of the vascular system through which the non-over-the-wire catheter is steered, the core wire (like the guide wire of the over-the-wire catheter) may develop a kink or may weaken due to fatiguing at this stress concentration point. These occurrences may make the non-over-the-wire difficult to steer and may unnecessarily prolong the angioplasty procedure. One such non-over-the-wire catheter is described in the European Patent Application Publication Number 0 368 523.
It is desirable in both over-the-wire and non-over-the-wire catheters to substantially eliminate the stress concentration point on the guide wire and core wire, respectively, between the relatively stiff bonded region at the distal end of the catheter and the flexible spring tip. The substantial elimination of this stress concentration point would significantly reduce, if not eliminate, kinking and weakening due to fatiguing of the wires.